1. Field of the Invention
The present invention relates generally to tubular prostheses, such as grafts, stents, stent-grafts, and the like. More particularly, the present invention provides radially expansible tubular prosthesis structures which can be expanded up to predetermined limits to match individual body lumens, including blood vessels, particularly for the treatment of abdominal and other aneurysms.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, lost occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and will equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently art elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay.
In Order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from undesirable limitations. In particular, proper sizing of endovascular prostheses can be problematic.
Proper matching of the prosthesis to the blood vessel is critical to the treatment of an aneurysm. The prosthesis preferably extends axially beyond the weakened portion of the blood vessel to anchor securely in the healthy vessel wall. However, the cross-sectional size and axial length of individual blood vessels vary considerably between patients. Even within a patient, the cross-section and resilience of a lumen wall can vary considerably along its axial length, and the location and extent of the aneurysm will differ with different patients. Additionally, each prosthesis must be carefully constructed and handled, making it extremely costly to provide and maintain the large selection of prostheses required for proper fitting of every individual patient.
Known radially expandable intraluminal prostheses may generally be characterized as either resilient or plastically expanded structures. Resilient intraluminal prostheses are often formed as stent-grafts having self-expanding frames or "stents" which radially conform to variations in lumenal cross-sections. Such resilient stent-grafts must expand against the luminal wall with sufficient force to anchor the prosthesis within the body lumen, and should ideally be sealed around the perimeter of the luminal wall to prevent leakage. Resilient prostheses which are too small may not expand sufficiently to seal or anchor properly, while oversized resilient prostheses can exert excessive pressure against the surrounding body lumen. Plastically expandable intraluminal prostheses have malleable frames which are expanded to fit the lumen when implanted, but the expanded prosthesis generally takes the cylindrical shape of the expanding balloon catheter, rather than conforming to irregular luminal cross-sections. Additionally, the expanded prostheses must be sufficiently large and rigid to provide a stable anchor and perimeter seal, requiring distension of the lumen adjacent the disease condition. Hence, even with proper fitting, most resilient or plastically expandable prostheses impose some stress on the body lumen. A still further complication arises from the use of a separate liner or "graft," which is often woven from inexpansible polyesters such as Dacron.TM., and which may therefore wrinkle and occlude the lumen if the stent graft is not fully expanded.
It has previously been proposed to use radially expansible liners with plastically expansible stents so that the liner and the frame may be expanded together within a body lumen. In particular, liner materials having undrawn or partially drawn yarns in the circumferential direction allow concurrent plastic expansion of the liner and frame using a balloon catheter. Such liner materials would thus facilitate in situ expansion of plastically expandable stent-grafts within a wide range of sizes. Unfortunately, because of the great expansibility of partially drawn yarns, any bulges formed by uneven expansion of the liner material may continue to expand in an uncontrolled manner during deployment or size adjustment. Such bulges in the liner may even result in a weak, oversized region that could potentially collect thrombus or even fail during deployment--effectively resulting in an aneurysm of the prosthesis. Furthermore, such bulges in an endoluminal prosthesis may cause folds of the liner material, leading to leakage between the prosthesis and the vessel wall.
Known prostheses having plastically expansible liner materials may suffer from additional disadvantages. As described above, such prostheses generally also include frames which are rigid hen expanded, typically relying on distension of the body lumen around a cylindrical frame to anchor and seal the prosthesis. Furthermore, undrawn or partially drawn liners may be inadvertently overexpanded, resulting in "creeping" of the material, changes in porosity, or even the creation of open fistulas. Any such overexpansion of the liner might well go undetected, as in situ expansion is generally a fluoroscopically directed process in which the condition of the liner is not easily monitored.
In co-pending U.S. patent application Ser. No. 08/538,706 (Attorney Docket No. 16380-38), which is assigned to the assignee of the present application, the full disclosure of which is incorporated herein by reference, describes a resiliently expandable prosthesis which includes a plastically expansible liner with a resilient frame, in which the resilient expansion of the frame is restrained by the liner. Advantageously, such a liner-restrained structure allows in situ expansion of the liner to match the perimeter of the surrounding body lumen, and also allows the fitted prosthesis to resiliently conform to irregular lumenal cross-sections. Application Ser. No. 08/538,706 also teaches the selective expansion of "sealing cuffs," integral or separate prosthetic end seals, which preferably include expansible liner materials to facilitate sealing and conforming an end of a tubular prosthesis against the surrounding body lumen wall. The use of liner materials with partially oriented yarns was suggested for these liner-restrained prostheses and sealing cuffs.
Although the liner-restrained prostheses, sealing cuffs, and partially drawn yarns described above provide substantial advantages over other endoluminal prosthetic structures, still further refinements are desirable. In general, it would be desirable to provide improved prostheses, including grafts and stent-grafts, and improved methods for placement of such prostheses to treat aneurysms and other conditions. It would be particularly desirable to provide liner materials for use in liner-restrained and other endoluminal prosthetic structures which would allow the prosthesis to expand plastically within a preset range, but which would reduce the danger of overexpansion. It would further be advantageous to provide liner materials which would allow controlled, selective expansion of portions of the prosthesis to promote anchoring or sealing, but which would resist expansion in alternative portions, particularly adjacent a weakened portion of a body lumen.
2. Description of the Background Art
U.S. Pat. No. 5,443,499 describes a radially expandable tubular prosthesis formed with radial yarns which are at most partially drawn. The prosthesis may optionally be secured to a bony lumen through simultaneous balloon expansion of the prosthesis and an attached stent. French Patent Application Publication No. FR 2,714,816 describes a vascular prosthesis including a sleeve which contracts axially when stretch ed radially. Sliding connections are provided between a support structure and the sleeve, and additional material is preferably provided to compensate for axial contraction of the sleeve. Similarly, U.S. Pat. No. 5,064,435 describes a self expanding prosthesis which maintains a stable axial length during expansion, by anchoring of radially outward flares at each end, and by sliding of an overlapping medial region therebetween. U.S. Pat. No. 4,834,755 describes a triaxially-braided fabric prosthesis structure to provide controlled strength and elasticity. U.S. Pat. No. 5,456,713 is generally relevant.
U.S. Pat. No. 5,258,042 describes an intravascular hydrogel implant which expands when hydrated. U.S. Pat. No. 5,470,313 describes a variable diameter balloon dilation catheter having a pressure controlled inflation profile.